The present invention relates to a drive device for an electric vehicle with an electric motor.
Examples of an electric vehicle include a hybrid electric vehicle in which a battery is charged by an engine, and which travels using a drive force of an electric motor driven by electrical power from the battery; a hybrid electric vehicle in which a battery is charged by an engine, and which travels using a drive force of an electric motor and (or) the engine; and an electric vehicle that travels using a drive force of an electric motor.
An electric vehicle is equipped with a parking lock mechanism that locks the gear of the electric vehicle in park by mechanically locking the rotation of a drive shaft connected to an electric motor. For example, the parking lock mechanism mechanically restricts the rotation of the drive shaft by moving a claw member via the operation of an electric switch, and making the claw member engage with a gear portion of the drive shaft or the like.
In the electric vehicle with the parking lock mechanism, when the electric vehicle is stopped on a hill, and the parking lock mechanism is brought into operation, the drive wheels (drive shaft) are mechanically locked, and thereby torsional torque occurs in the drive shaft due to a rotating force of the drive wheels. For example, when the electric vehicle is stopped on a hill facing downward, a forward rotating force occurs in the drive shaft, and torsional torque occurs and is accumulated.
There is a problem in that the release of the parking lock mechanism for driving away the electric vehicle causes the rapid release of the torsional torque, and then the occurrence of a shock. In order to solve this problem, in the related art, there is proposed a technology by which drive means is driven to apply torque in the opposite direction of the direction of the torsional torque when the parking lock mechanism is released (for example, refer to Patent Document 1). The use of the technology disclosed in Patent Document 1 prevents a shock from occurring when the torsional torque is released.
However, according to the technology disclosed in Patent Document 1, the magnitude of torque applied in the opposite direction of the direction of torsional torque accumulated in the drive shaft is estimated from mechanical characteristics of the drive shaft or the like when a drive force is transmitted thereto. For this reason, there is a problem in that depending on the hill, or a state at the time of torque estimation, a large difference may occur between the magnitude of the estimated torque and the magnitude of the opposite directional torque that is actually required. Accordingly, in reality, it may not be possible to accurately and satisfactorily prevent the occurrence of a shock when the parking lock mechanism is released.
[Patent Document 1] Japanese Patent No. 4297135